[Dragon]

I was strictly speaking about the FTL aspect of it. Regarding a more modest objective I do not possess enough knowledge to know one way or the other, but the mechanism sounds energetically costly (euphemism) and overall crazy. I'm not expecting Elon Musk presenting the Alcubierre Drive in the next 50 years for the Falcon 23.

Just a note, "Falcon 23" would imply a 23-engine monstrosity along the lines of the old N1 rocket. Elon probably knows better than to try that. Also, Alcubierre drive isn't much good as a liftoff engine, so if developed, it'd probably go on a Dragon. And the effect is being studied by NASA (look up dr. Harold White). The energy cost might not be as big as it seems. Bending spacetime to do our bidding does sound crazy, but noone who ever achieved anything said "this is crazy, it'll never work" (well, maybe except for a brief exclamation when working out the kinks of the new idea). Turns out it's already been successfully done in small scale, and it apparently didn't black out the continent, so maybe the energy requirements aren't that bad.

Also, while FTL version is the one people are the most excited about, STL one is based on actually proven physics (well, it works, or at least seems to) and either way, an important stepping stone towards FTL one, should the latter be possible. Even if it doesn't, there's a lot of potential in this form of propulsion, especially since it isn't restricted by Newton's 3rd law. Alcubierre drive is essentially reactionless, so neither the Tsiolkovsky Rocket Equation nor Newton's equations limit it's efficiency. It's not like there are no other limiting factors, but it's something to consider.

[Phantom Hoover]

oh man i can't resist

"700kg of energy" is what you get from fusing 450kg of matter with 450kg of antimatter.

[Phantom Hoover]

oh nb this isn't even true on any level, depending on the type of matter you use an annihilation reaction will produce neutrinos; so you're right back where you started

[Dragon]

oh man i can't resist

I'd strongly advise you to do so, because you're wrong.

What I said is true. 700kg of matter can literally be equated to 700kg of energy. That's what E=mc² means, unless you're one of the ones who don't accept Relativity. 350kg of antimatter+350kg of matter, when anihilating, will release that energy, generally in some other form than matter an antimatter. Now, for my simplistic example I assumed that you end up with a handful of "pure energy" (photons, they have no rest mass, only kinetic and potential energy). Now, about the only true thing you said is that you can also get neutrinos out of that; they do have rest mass, which means you get (kinetic and potential) energy + mass of neutrinos. I didn't get into this, since it's not useful for explaining why mass is a form of energy, and therefore one can be expressed using units for other.

In general, there are 3 kinds of energy in the universe. There's kinetic energy, potential energy and mass. They can and often do change into one another, and can be measured with the same units. For extra fun, try also expressing time in meters, since you can also do that thanks to relativity. The laws of the universe become surprisingly beautiful in this form, and you don't need to fully delve into natural units (which will make your head hurt until you get used to them).

Now, the problems of getting useful energy out of an A-M reaction is another thing entirely. I won't delve into that. You evidently mixed up with what I wanted to say, since neutrinos are indeed pretty useless as far as power generation goes. So are very high energy photons (gamma rays). They just pass through the collector. But exactly what you get depends on what you put in, and I'm pretty sure there's a reaction that could work for power generation with good efficiency.

[The E]

450kg + 450kg = 900kg.

Also, where the hell are you getting (and storing) 450kgs of AM?

[Dragon]

Bah, that's what I get for doing everything in Mathematica these days. Fixed. I've got that problem a lot, I properly split and calculate a triple integral, then I screw up addition or mix up something equally trivial. In my defense, I'm not the only one with this problem (you usually let Mathematica put in numbers once you know how the equations look like, so it's not a big handicap). But you're right, I should've probably double-checked the post.
As for how to get 350kg of AM, that's just theoretical divagations, while it's nothing that can't be done physics-wise, it's obviously quite hard to do if you actually tried to launch such a ship. So's a propulsion-scale STL Alcubierre drive, but it's not like it ever stopped anyone from discussing it.

[The E]

Excuse me for thinking that discussing the practical issues with actually building and powering an Alcubierre drive are a necessary part of any discussion involving Alcubierre drives.

[Dragon]

TBH, I didn't intend that particular idea to serve as a power source - just explaining what "700kg of energy" is. About 63000 petajoules, or 4*10³⁸ electronovolts, or 6.3*10²⁶ ergs, or even 6*10¹⁶ BTU. Whatever. A tremendous amount of energy, but it doesn't seem impossible. Now, we go find some good fusion fuel. According to AtomicRockets, D+He3 gives us 353.23 TJ/Kg. Now it's a rather trivial division to find we'll need about 180T of fusion fuel, assuming we can reclaim 100% energy produced (or that AtomicRocket counted in the loss in it's figure). That's a lot, but there's much more water on Earth than that. He3 could be a problem, if you want to propose a different fuel mix, just give me the numbers for it (gotta love Mathematica, once you come up with a routine, you can run it for any good data). Now the question boils down to two factors: making fusion power work and lifting 180T or something of fuel into space. Soviets could've had the capacity to do the latter by the 90s (proposed Energia-Vulkan booster could probably make that much to LEO) if it wasn't for politics, so could US with the Nova rocket. The former is being researched and we're making good progress. So we could probably power the thing by fusion just fine.

Now, could we afford this? Nope, not today. But someday it might change. It's definitely not physically impossible, even with 10 times less efficient fusion reaction (D-T, for example), it boils down to an engineering problem, and one that can be solved "brute force" by building more superheavy LVs. Also, 700kg is for an FTL version, I imagine that the STL one would be much cheaper in terms of energy.

I think that discussing engineering details of a car before the idea of a wheel has been fully proven is somewhat far-fetched, but if White's research is enough of a proof for you, we can talk that, sure. But IMO, it's a whole different discussion.

One nice thing is, I noticed one problem with the concept thanks to this discussion. Assuming it's an actual proposal, there's no way it could run on fusion, there's not enough space for fuel tanks. 180T of light elements, even if you liquefy them, takes a lot of space. Now, Star Trek ships are A-M powered, but as you highlighted, I'd rather take my chances with 72T of deuterium and 108T of He3, and building an efficient fusion reactor.

[Ace]

The STL probe version can probably run on fusion, but you'd definitely need an AM powerplant and engine (along with solar infrastucture to generate the AM fuel) to go faster.

Honestly, it seems that the FTL version really needs a space elevator due to sheer tonnage. Since not only do you need the powerplant and exotic matter ring, you then have the hab module, and reaction mass. (300-400t ship?)

Now wait, before you go "crazy scifi things needs another one!" With current materials science we have the tensile strength to build an elevator in a lower gravity well like the moon. One on Earth may be "10 years away, forever" though.

So, lunar or martian elevator and assembly for a starship makes the most sense.

AM v.s. fusion, if something goes wrong you're dead anyway so I don't see a reason to prefer the less efficient form of energy storage.

[Dragon]

Dunno about reaction mass. While it's true Alcubierre drive doesn't accelerate you by itself in physical sense, reaction mass required depends on what you want to do. With a plasma-based heatshield (because if you've got fusion, you should be able to do that, too), you could try for an aerocapture at your destination, therefore you might only need a bit of xenon for ion-based RCS system (hey, you're running of fusion, you're not short on electrical power!). The ship's gonna be heavy, but I don't think that a space elevator is a strict necessity. It'd slash the launch costs immensely, but if you're not scared of nukes, gas core-engined LV could be enough to handle the logistics.

And as I said, if the "700kg of energy" requirement holds, running the FTL version of fusion doesn't seem so impossible anymore. I'm not sure what's the relation between this energy and mass of spacecraft (there being no relation would likely be too good to be true...), but launching 200-400T to LEO can be done with todays' technology, albeit at quite a cost (which Elon Musk is soon gonna drive down, BTW. Methane is cheap).

[Bobboau]

and the 700Kg energy requirement is recently down from the mass of Jupiter, which was down from 'more energy than the visible universe' so we've been seeing a progressing trend in the direction this thing is going in.

[Kopachris]

...

So, lunar or martian elevator and assembly for a starship makes the most sense.

...

Utopia Planitia Shipyards, here I come!

[666maslo666]

Also, while FTL version is the one people are the most excited about, STL one is based on actually proven physics (well, it works, or at least seems to) and either way, an important stepping stone towards FTL one, should the latter be possible.

According to wiki the results are inconclusive..

https://en.wikipedia.org/wiki/Talk%3AWhite%E2%80%93Juday_warp-field_interferometer

Remember, though, antimatter (essentially "negative matter" from a certain point of view, though with positive mass) and neutrinos started out that way, too, as did Higgs bosons and many other heavy particles, so I'm optimistic.

I am just an armchair physicist but I am not aware of any evidence that negative mass is plausible, either experimental or theoretical. While Higgs bosons or antimatter was predicted as likely existing, so thats different. There are lots of particles that could exist in some farfetched theory but dont exist in reality.

I also found this article by a string theorist highly critical of FTL Alcubierre drive concept:

http://motls.blogspot.sk/2013/07/relativity-bans-faster-than-light-warp.html

[Black Wolf]

I also found this article by a string theorist highly critical of FTL Alcubierre drive concept:

http://motls.blogspot.sk/2013/07/relativity-bans-faster-than-light-warp.html

He's also a climate change denialist. Although it shouldn't affect the way I read his physics (and his statements certainly seem to make sense in that article, even though I wish they didn't), it kinda makes me wonder about his scientific nonce.

[Phantom Hoover]

Motl suffers from the tragically common affliction in physicists and engineers and architects of thinking he can understand absolutely anything based on his aptitude at physics.

[Dragon]

He's also, as has been said, a string theorist, not a relativist. White, on the other hand, actually specializes in what he's doing. I think that he already considered points raised in the article. While it does make sense, the restrictions mentioned all seem awfully basic. It's not something you just miss, while layman's understanding of a warp drive does indeed boil down to what was "debunked", I'm sure White's approach already took those restrictions into account. He simply wouldn't be working on something so trivially impossible.

As for the interferometer experiment being inconclusive, I wouldn't despair. They did notice a tendency, even if it isn't strong enough to actually bring a solid conclusion, it's probably just a matter of building a bigger/more precise interferometer. I'd say, give them time, given the scale of the experiment, it's to be expected that the effect would not be very strong.

[Ace]

Also, while FTL version is the one people are the most excited about, STL one is based on actually proven physics (well, it works, or at least seems to) and either way, an important stepping stone towards FTL one, should the latter be possible.

According to wiki the results are inconclusive..

https://en.wikipedia.org/wiki/Talk%3AWhite%E2%80%93Juday_warp-field_interferometer

Remember, though, antimatter (essentially "negative matter" from a certain point of view, though with positive mass) and neutrinos started out that way, too, as did Higgs bosons and many other heavy particles, so I'm optimistic.

I am just an armchair physicist but I am not aware of any evidence that negative mass is plausible, either experimental or theoretical. While Higgs bosons or antimatter was predicted as likely existing, so thats different. There are lots of particles that could exist in some farfetched theory but dont exist in reality.

I also found this article by a string theorist highly critical of FTL Alcubierre drive concept:

http://motls.blogspot.sk/2013/07/relativity-bans-faster-than-light-warp.html

Well, we have literally no idea what dark energy is. But if it is negative energy, that means negative mass can potentially exist.

[Black Wolf]

Dark matter and dark energy both... Kinda feel phlogiston-ish to me, although I freely admit I don't have the physics background to back that up. Has there been any conclusive evidence yet to rule out a MOND-like modification of long range gravitational effects?

[Bobboau]

I believe this is generally considered the piece of evidence that finally killed MOND.

[deathfun]

So that ship model looks pretty cool
Makes me kinda want to start modeling stuff again and putting it in Freespace